Accepted Answer

Omni Air Dash lets you move in any direction, by pressing R+Triangle and a direction you want to go in. If you do not press a direction I believe it takes you towards your opponent automatically. However, you can only go in a horizontal direction, you can't go vertical (you can go forward, back, sideways, but not up and down). This makes its usage a liiittle more limited than you might think. If you lock onto an EX core, however, you WILL be able to get up/down towards it automatically (don't press a direction).

The ability that uses X is Multi-air Slide (all characters) or Glide (which is Kuja-only in normal mode, and a few other characters can do it in EX mode) Multi-air slide is a quick dash in any direction that you can do by pressing X after using up all your jumps. Again, this is horizontal only. Glide lets you float from side-do side by holding X, however few characters actually have this ability, so I haven't used it much myself.

Hopefully that covers what you were asking, but if not, then maybe you can give a better description of your problem.